Beyonce, only 22, is furious because 28-year-old Blu said she's already shared a kiss with Jay-Z -- even though she is well aware that Beyonce's involvement with the rapper is serious.

"Blu says she likes to say what's on her mind and doesn't care what anybody thinks," revealed an insider.

In the shocking interview, released on the DVD that accompanies her new album, Blu blathers that Jay-Z is "such honey. He's just a doll baby. I don't care who he is dating -- I've always had a crush on him."

She acknowledges that Beyonce and Jay-Z are in love, but asked what she would do if he propositioned her, Blu admitted, "I wouldn't turn it down, let's just put it that way!"

Divulged the insider: "Beyonce felt that was a slap in the face and she didn't appreciate it one bit.

"She let Jay-Z know she loves him, trusts him and respects him -- but she does not want him to hang out with Blu under any circumstances."

Happily, the insider insists Beyonce has nothing to worry about because her 33-year-old boyfriend is "a one-woman man. Jay-Z is not going anywhere -- not even for one night."